The dramatic increase in usage of personal computers, workstations, and servers to perform every sort of daily task in recent decades has meant that the speed at which computer systems operate has become very important. The speed at which a computer system carries out the execution of an application is largely dependent on the speed of the operating system. An operating system in a modern computer system controls and monitors the use of hardware resources and provides programming interfaces to applications.
One process that slows down the performance of an operating system and the applications installed on a computer system is the process of suspending the execution of the operating system to conduct certain input and output (I/O) related operations. Such a suspension often occurs when files are opened. In order to open a file, an operating system must determine a “path” to the file by accessing a namespace in the file system. Accessing the namespace in the file system suspends execution of operating system tasks. However, once a file has been accessed the first time, the path for the file is typically cached in memory, so that future accesses of the file, at least for a time, do not cause the operating system to suspend execution of tasks. An operation that does not cause the operating system to suspend the execution of tasks is often referred to as an “atomic” operation.
Applications do not have a way, at execution time, of knowing if a file system path is stored in memory or not. An application must simply ask the operating system to open the file. An application developer must simply live with the possibility that a serious performance or scheduling impact will result if the operating system must determine the file path from the file system namespace, and hope that at least in some cases, the opening of the file will be able to proceed atomically.